EXPEDITION OF THE CHALLENGER. 45 



the fewer signs are there of convergence toward the iirimitive form 

 whence all must have diverged, if evolution be a fact. Nevertheless, 

 that it is a fact in some cases, is proved, and I, for one, have not the 

 courage to sUpi)Ose that the mode in which some species have taken 

 their origin is different from that in which the rest have originated. 



What, then, has become of all the marine animals Avhich, on the 

 113'pothesis of evolution, must have existed in myriads in those seas, 

 wherein the many thousand feet of Cambrian and Laurentian rocks, 

 now devoid, or almost devoid, of any trace of life, were deposited ? 



Sir Charles Lyell long ago suggested that the azoic character of 

 these ancient formations might be due to the fact that they had un- 

 dergone extensive metamorphosis ; and readers of the " Principles of 

 Geology " will be familiar with the ingenious manner in which he con- 

 trasts the theory of the Gnome, who is acquainted only with the in- 

 terior of the earth, with those of ordinaiy philosophers, who know 

 only its exterioi*. 



The metamorphism contemplated by the great modern champion 

 of rational geology is, mainly, that brought about by the exposure of 

 rocks to subterranean heat, and, where no such heat could be shown 

 to have operated, his opponents assumed that no metamorphosis could 

 have taken place. But the formation of greensand, and still more 

 that of the " red clay " (if the Challenger hypothesis be correct) affords 

 an insight into a new kind of metamorphosis not igneous, but aque- 

 ous by which the primitive nature of a deposit may be masked as 

 completely as it can be by the agency of heat. And, as Wyville 

 Thomson suggests, in the passage I have quoted above (p. 17), it 

 further enables us to assign a new cause for the occurrence, so puz- 

 zling hitherto, of thousands of feet of unfossiliferous fine-grained 

 schists and slates, in the midst of formations deposited in seas which 

 certainly abounded in life. If the great deposit of " red clay " now 

 forming in the eastern valley of the Atlantic were metamorphosed 

 into slate and then upheaved, it would constitute an " azoic " rock of 

 enormous extent. And yet that rock is now forming in the midst of 

 a sea which swarms with living beings, the great majority of which 

 are provided with calcareous or silicious shells and skeletons, and 

 therefore are such as, up to this time, we should have termed emi- 

 nently preservable. 



Thus the discoveries made by the Challenger expedition, like all 

 recent advances in our knowledge of the phenomena of biology, or of 

 the changes now being effected in the structure of the sui-face of the 

 earth, are in accordance Avith, and lend strong support to, that doc- 

 trine of Uniformitarianism, which, fifty years ago, was held only by a 

 small minority of English geologists Lyell, Scrope, and De la Beche 

 but now, thanks to the long-continued labors of the first two, and 

 mainly to those of Sir Charles Lyell, has gradually passed from the 

 position of a heresy to that of catholic doctrine. 



